A TPMS (Tire Pressure Monitoring System) functions to detect the air pressure of tires attached to a vehicle, and to issue a warning or the like to a user in the case where the detected air pressure is abnormal. The TPMS includes an in-vehicle wireless device that detects the air pressure of a tire and wirelessly transmits a signal indicating the detected air pressure using radio waves in the UHF band, an in-vehicle communication apparatus that is provided in the vehicle and receives the signal wirelessly transmitted from the in-vehicle wireless device, and a reporting apparatus that reports the air pressure that is indicated by the received signal.
However, the frequency band of the signal that is transmitted by the in-vehicle wireless device of the TPMS is the same as the frequency band of the signal that is transmitted by a mobile device, that is, an electronic key, constituting a passive entry system, a keyless entry system, a smart start system or the like, possibly resulting in crosstalk. Crosstalk may cause a malfunction of a passive entry system or the like. Crosstalk may also cause a malfunction of a tire pressure monitoring system.
An object of the present invention is to provide a vehicular communication system and an in-vehicle communication apparatus that are able to prevent crosstalk between signals that are transmitted from an in-vehicle wireless device constituting one wireless communication system such as a TPMS and a mobile device constituting another wireless communication system.